Changes in the Epilimnetic Bacterial Community Composition, Production, and Protist-Induced Mortality along the Longitudinal Axis of a Highly Eutrophic Reservoir

Abstract

A B S T R A C TWe studied changes in the epilimnetic bacterial community composition (BCC), bacterial biomass and production, and protistan succession and bacterivory along the longitudinal axis of the canyonshaped, highly eutrophic Sau Reservoir (NE Spain) during two sampling campaigns, in April and July 1997. Longitudinal changes in BCC from the river inflow to the dam area of the reservoir were detected by using oligonucleotide probes targeted to the kingdom Bacteria, to the alpha, beta, and gamma subclasses (ALFA, BETA, and GAMA) of the class Proteobacteria, and to the Cytophaga/ Flavobacterium (CF) cluster. In general, the inflow of the organically loaded Ter river, with highly abundant allochthonous bacterial populations, induced a clearly distinguishable longitudinal succession of the structure of the microbial food web. The most dynamic changes in microbial parameters occurred at the plunge point, the mixing area of river water and the reservoir epilimnion. Changes within members of BETA and CF were the most important in determining changes in BCC, bacterial abundance and biomass. Much less relevant changes occurred within the less abundant ALFA and GAMA bacteria. From the plunge point downstream, we described a significant shift in BCC in the form of decreased proportions of BETA and CF. This shift spatially coincided with the highest values of heterotrophic nanoflagellate bacterivory (roughly doubled the bacterial production). CF numerically dominated throughout the reservoir without any marked longitudinal changes in their mean cell volume. In contrast, very large cells affiliated to BETA clearly dominated in the allochthonous bacterial biomass brought by the river. BETA showed a marked downstream trend of decreasing mean cell volume. We conclude that the observed BCC shift and the longitudinal shift in food web structure (bacteria-heterotrophic nanoflagellates-ciliates) resulted from highly complex interactions brought about by several major factors: varying hydrology, the high localized allochthonous input of organic matter brought by the river, downstream changing substrate availability, and selective protistan bacterivory.

GIS-based analysis of the fate of waste-related pathogens Cryptosporidium parvum, Giardia lamblia and Escherichia coli in a tropical canal network

“…These mechanisms are assumed to include a large scale sedimentation (Grimason et al 1993), as was confirmed by the presence of the pathogens in the sediment. Table 2 and/or invertebrates (Fayer et al 2000;Simek et al 2001;Stott et al 2001). Overall, the removal of G. lamblia was greater than that of C. parvum, comparing well with literature.…”

Influence of inlet bacteria on bacterioplankton assemblage composition in lakes of different hydraulic retention time

“…Statistical evaluations of DGGE patterns have shown correlations to the grazer abundance in several lake studies (Lindström 2000(Lindström , 2001Muylaert et al 2002). Also, in experimental studies, it has been shown that grazers are capable of shaping bacterioplankton assemblage composition (e.g., Simek et al 1997;Hahn and Höfle 1998;Gasol et al 2002). Therefore, differences in grazing pressure may also have had some influence on the differences in bacterioplankton communities between lakes and inlets.…”

“…That such factors also may influence the composition of bacterial assemblages is likely (e.g., Methé and Zehr 1999;Simek et al 2001a;Lindström and Leskinen 2002;Muylaert et al 2002;Crump et al 2003;Stepanauskas et al 2003). Here we show that the import of the bacteria themselves also may contribute to the structure of lake bacterioplankton assemblages.…”

“…Experiments have shown a low survival of allochthonous bacteria in freshwater mesocosms (e.g., Höfle 1992; Leff et al 1998). In reservoirs, the influence by allochthonous bacteria has been found to be local (Simek et al 2001a;Gasol et al 2002) or low (Dumestre et al 2002). On the other hand, results from a few natural freshwater systems have indicated that allochthonous bacteria can influence the assemblage composition of the bacterioplankton (Lindström 1998(Lindström , 2001Crump et al 2003;Stepanauskas et al 2003).…”

Dissolved oxygen response to wind‐inflow interactions in a stratified reservoir

“…Reynolds et al (2002) realized that this influence is strong enough to allow functional classification of phytoplankton largely on the basis of characteristics of the physical environment. Moreover, spatial and temporal variability of ecological processes in lakes and the ocean have been associated with a wide range of physical processes: longitudinal shear dispersion (Okubo 1980;Martin 2003), vertical shear dispersion (Martin 2003;Cowles 2004), internal wave oscillations (Franks 1995), wind-induced upwelling (Robarts et al 1998), internal wave breaking (MacIntyre et al 1999), and buoyancy-driven inflows (Serruya 1974;Š imek et al 2001), to name a few. In man-made lakes, the water quality and ecology is often regulated by the characteristics of the inflowing rivers carrying nutrients and organic matter into a lake Friedl and Wü est 2002;Masin et al 2003).…”